The display of messages and indicia on a fan is disclosed in U.S. Pat. No. 7,161,256 to Fang, hereby incorporated by reference as though fully rewritten herein. The '265 patent discloses light-emitting elements mounted directly on a fan that can be controlled to generate various different twinkling light-image variations, utilizing the effect of persistence of vision when the fan motor is rotating. U.S. Pat. No. 6,480,116 to Wang, hereby incorporated by reference as though fully rewritten herein, discloses a “Method and Apparatus for Showing Special Characters or Figures on a Rotating Disk.” The '116 patent discloses illuminating a rotating disk in a manner such that the rotational cycle of the disk is analyzed and different light fittings on the rotating disk light up at various time delays dependent in part upon the persistency of vision of the human eye, thereby displaying figures or special characters. The terminology “persistency of the human eye” relates to the principle that when a bright image is viewed by the human eye, the brain will perceive the image still to be there for a short time after it has been removed. U.S. Pat. No. 6,175,354 to Bissett discloses an “Image Display Apparatus,” wherein LEDs positioned on fan blades are selectively energized. The '354 patent further discloses a counter and a microcontroller which measure the time the fan blades take to complete a full cycle of rotation, calculate a delay time when no image is displayed, and selectively energize the LEDs according to a pattern or digitized image stored in memory. U.S. Pat. No. 6,213,617 to Barker, hereby incorporated by reference as though fully rewritten herein, discloses the illumination of a fan by strobe lights positioned at substantially equal spaced apart distances around the central body portion of the fan assembly to project light onto the fan blades. An electric eye emitter and sensor detect the fan blade location in order to determine the angular rotation and position of the fan blades in order to synchronize the operation of the strobe lights with the fan blades. U.S. Pat. No. 7,179,149 to Chernick discloses a novelty lighting device that spins in a variety of circular pathways with a control circuit that selectively flashes the lights in an array in a manner that is synchronized to the speed of the various lights in their circular pathways.
Lasers have been utilized to measure the velocities and blade attitude of a helicopter blade in wind tunnels as disclosed in the article entitled “2D Laser Velocimetry Near Helicopter Blades in DNW (NLR),” by Boutier, et al, Instrumentation in Aerospace Simulation Facilities, 1993. ICIASF '93 Record, International Congress on Sep. 20-23, 1993 Page(s) 321-328, hereby incorporated by reference as though rewritten herein. The Boutier article describes tests achieved at DNW (windtunnel of NLR) on a helicopter in forward flight conditions for the purposes of recording the components of the velocity vector in a 2D vertical frame around the blade, and simultaneously measuring the position of the 2 m long blade rotating at a speed of 1050 rpm. Two series of measurements were performed: the first one in a closed test section (8 m×10 m) with a working distance of 2.7 m, the second one in an open test section for which this working distance was increased up to 5 m. The Boutier article describes the optical and mechanical set-up, the synchronization of the measurements and the blade attitude measurement technique and presents results of the determination of the velocity field around helicopter blades in forward flight conditions with the attitude of the blade extremity being simultaneously recorded on the same computer.
The blades of a helicopter are somewhat unique in terms of the aerodynamics of the fuselage and blades. Helicopters experience unique forces when in flight, and the blades are designed to overcome and/or compensate for such forces. As a helicopter moves forward, the tip speed changes as the blades rotate around the fuselage. An increase in tip speed occurs when the blade advances toward the nose in the direction of flight, since the velocity of the helicopter adds speed to the velocity of the tip. As the tip begins retreating past the helicopter, the tip speed decreases inasmuch as the speed of the helicopter is subtracted from the tip speed. Because lift increases with airflow speed, the advancing blade produces more lift than the retreating blade, resulting in the need to make adjustments to prevent roll over.
To compensate for the unbalanced lift the blades are flexible, or articulated. Each main rotor blade is connected to the shaft by a flexible hinge, allowing the rotor blades to rise and fall slightly as they rotate, resulting in flapping. The retreating blade, creating less lift, naturally flaps down so as to increase lift. Flapping allows the differences in lift caused by uneven rotor tip speed to cancel out, producing a stable ride. In addition, during the operation of the helicopter, the pilot will change the angle or pitch of the blades in order to maneuver the helicopter. In general, a collective pitch stick or lever allows the helicopter to climb and descend vertically by changing the pitch of all the main rotor blades equally. Pulling or pushing on the lever increases or decreases the thrust produced, varying the lift.
Helicopters are adapted to be used for various missions, including search and rescue, traffic observation and reporting, and military operations involving delivery and retrieval of personnel. During such missions, communication between ground-based personnel and helicopter crews is essential. For example, rescue helicopters rescuing water bound persons may need to give instructions to the person floating in the water below, when speaker projection systems may be insufficient in producing sufficient signal to noise ratios to overcome the helicopter and surf noise
In traffic reporting applications, helicopters may need to communicate directly with ground-based people not in possession of a radio, or to communicate directional information difficult to express orally.
In certain military operations, it is desired to deliver military personnel to covert or dangerous locations. To achieve covert insertions, or to deliver personnel quickly, conventional operations often involve delivery of personnel to the ground via ropes extending from the helicopter to the ground, obviating the need landing the helicopter. However, soldiers that fast-rope from a helicopter are often disoriented during the insertion process, and unable to determine the proper direction of travel on reaching the ground. Although radio communication is sometime used to assist the ground personnel, radios are not issued to every ground soldier, and often the communication between aircraft and ground crew is difficult due to environment and operational distractions.
In view of the difficulties of communication conventionally encountered between in-flight helicopters and ground-based personnel, it is an object of the present invention to provide a system and method to enable visual communication between helicopter crews and ground-based personnel. In particular, it is an object of the present invention to provide a system capable of projecting images and/or messages via a laser light source on the underside of rotating helicopter blades. These messages or icons can also represent geospatial references relative to the helicopter, or some ground way point.